Once you have begun to collect links on the internet, you will find that you would like to access them anywhere and on any device that access the internet. This is where social bookmarking comes in. Diigo or delicious are two of the most popular social bookmarking sites and each offer similar but slightly different options and capability.
Relatively speaking delicious is easier to start out with however Diigo offers the capability to annotate over and highlight aspects of the pages being linked to. In addition Diigo users can create groups to share bookmarks within and make Lists of bookmarks to share with students. Diigo users can also automatically add new bookmarks to a delicious account and/or blog. Diigo also offerseducators' accounts.
To see what each service offers, click here to access my delicious account and my my Diigo account

Here's a movie that will guide you through more of the capabilities of Diigo.


You could also check out the Diigo help. and maybe the Bright Ideas YouTube series on Diigo.
Here's some ideas on using Diigo in the Classroom, (plus also Storify).